DE69216777T2 - Process for the treatment of milk that preserves its suitability for cheese making - Google Patents

Abstract

The milk (1) is subjected to a microfiltration-diafiltration (2), then to a heat treatment (3) and finally to an ultrafiltration (4) in order to obtain a product (5). This product can, under excellent conditions, be processed into cheese.

Description

The subject of the present invention is a process for treating milk and other dairy raw materials suitable for being converted into cheese, the process making it possible to preserve or even improve their suitability for cheese production.

In the traditional cheese-making processes, the intensity of the thermal treatments applied to the milk used to make the cheese varies according to the applications, but generally lies within a temperature range of 65 ºC to 90 ºC for a period of 10 s to 10 min.

These treatments allow the elimination of the harmless and pathogenic flora of the milk.

In order to eliminate the spore-forming flora and in particular Clostridium tyrobutyricum, which are responsible for the delayed swelling in the cooked, pressed dough technology, it is necessary to use treatments at high temperatures of the order of 110-160 ºC for a few seconds, O. CERF, J. HERMIER (1973), Abnormal thermoresistance of bacterial spores heated by direct injection in steam. Le Lait, 53, 23-29.

Cheese professionals are well aware of the disadvantages of applying intensive thermal treatments to milk intended for cheese production. Numerous studies have shown a decrease in the suitability of thermally treated milk for its Conversion into cheese demonstrated: see in particular ME POWELL, LS PALMER (1935), Behaviour of caseinate sols in a study of a hysteresis like phenomenon in the rennet coagulation of heated milk. J. Dairy Sci, 18, 401-416, and GT PYNE (1945), Rennet hysteresis and the calcium phosphate of milk. Biochem. J., 39, 385.

One of the main phenomena implied by this decrease in the suitability for coagulation of thermally treated milk is the interaction between the soluble proteins (α-lactalbumin and β-lactoglobulin) and the caseins through the activation of the SH groups and through the formation of disulfur bonds and hydrophobic bonds. This interaction is due to the formation of complexes between β-lactoglobulin and χ-casein.

It has been shown (C. FERRON-BAUMY, J. L. MAUBOIS, G. GARRIC, J. P. QUIBLIER (1991), Coagulation presure du lait et des rétentats d'ultrafiltration. Effets de divers traitements thermiques. Le lait, 71, in press) that the primary coagulation phase by the rennet (as estimated by the kinetics of the release of caseinomacropeptide) in a warmed milk at an elevated temperature proceeds perfectly normally, i.e. that the primary coagulation phase is not disturbed by the heating. However, one notes a decrease in the initial reaction rate of the order of 30% and a decrease in the final caseinomacropeptide content of 20%. The decrease in the ability to coagulate or the absence of coagulation cannot therefore be attributed to this phenomenon.

The binding of β-lactoglobulin to χ-casein causes an increase in the negative net charge of the casein micelles (1. M. REDDY, JE KINSELLA (1990), Interaction of β-lactoglobulin with the K-casein in micelles as assessed by chymosin hydrolysis : effect of temperature, heating time, β-lactoglobulin concentration and pH J. Agric. Food Chem., 38, 50-58). In addition, the steric space requirement of the complex counteracts the effect of the rennet (EJ HINDLE, JV WHEELOCK (1970). The primary phase of rennin action in heat-sterilized milk. J. Dairy Res, 37, 389-396) and (ACM VAN HOOYDONK, C. OLIEMMN, HG HAGEDOORN (1984), Kinetics of the chymosin-catalyzed proteolysis of K-casein in milk. Neth. Milk Dairy J., 37, 207-222).

Another consequence of intensive thermal treatment is a significant decrease in the soluble calcium content, which limits the formation of bonds between micelles during the formation and thickening of the curd. The curd formed is therefore more fragile (crumbly) and less suitable for mechanical processing such as cutting and stirring.

In order to solve these problems of non-coagulability or poor coagulability of heated milk and to enable its use in cheese making, several processes have been proposed which aim either at reducing the charge of the casein micelles or at limiting the formation of the β-lactoglobulin-χ-casein complex by depleting the milk of part of its soluble proteins or by limiting the denaturation of serum proteins or by enriching the milk in ionized calcium.

A first group of known methods includes the techniques for reducing the charge of casein micelles:

- by acidification: see H. SINGH, SI SHALABI, PF FOX, A. FLYNN, A. BARRY (1988), Rennet coagulation of heated milk: influence of pH adjustments before and after heating. J. Dairy Sci., 55, 205-215. These authors have developed a technique to restore the coagulation capacity of heated milk by adjusting the pH of the milk before or after the thermal treatment. Upstream or downstream of the thermal treatment they practice acidification up to a pH of 5.5-6.0, followed by neutralization to a pH of 6.6. This technique allows the milk to be coagulated again by acting on its mineral balance. It has a Enrichment of milk with ionised calcium. The shortcomings in terms of bitterness in cheddar technology resulting from this practice have been pointed out: JM BANKS (1988), Elimination of the development of bitter flavour in cheddar cheese made from milk containing heatdenatured whey protein . J. Soc. Dairy Technol., 41, 37-41.

- by adding calcium chloride: see R. J. MARSHALL (1986), Improving cheese yields by high heat treatment of milk. J. Dairy Res., 53, 313-322. This article describes the manufacture of Cheshire-type cheese from milk heated to 97 ºC for 15 s, which enriches the milk with soluble calcium and reduces the pH to 6.40. A normal coagulation time was then observed for the milk thus acidified, but the curd had a high water content. This process cannot be used to make any type of cheese. It does not enable milk to be fully restored to its suitability for transformation into cheese.

Techniques leading to a relative lowering of the surface charge of the micelles by partial concentration of the milk by ultrafiltration have also been proposed. The partial concentration of UHT milk by ultrafiltration (JL MAUBOIS, G. MOCQUOT, L. VASSAL (1973), Patent FR-73 07 117. Procédé de traitement du lait et de sous-produits laitiers) allows a coagulation time of the milk in the order of 30-40 min. However, the strength of the coagulate obtained is not entirely satisfactory for the technologies of boiled, pressed dough.

Another category concerns techniques to reduce the formation of the β-lactoglobulin-χ-casein complex;

- the HHT (high heat treatment) procedure consists in limiting the denaturation of serum proteins, in particular β-lactoglobulin. The HHT process (see in particular D. TROSSAT (1980), Realization and study of the characteristics of an HHT type milk sterilization device by direct steam injection. Doctor-Ing. ENSAM thesis, Paris; C. FABRE (1982), Study of a rapid steam condensation system in a coulomb-filled liquid for milk sterilization. Doctor-Ing. thesis, INPL, Nancy; C. ESNOUF, E. ABOU MANSOUR (1990): A new steam injection process: application of the mixture to the pore of a new thermal milk treatment. Le Lait, 70, 233-254) uses thermal treatments at high temperatures for a few fractions of a second. The hygienic effectiveness obtained by this process is comparable to that obtained by UHT treatment, although the denaturation of soluble proteins occurs to a lesser extent during HHT treatment. It occurs in the order of 25-30% for β-lactoglobulin. This weak denaturation of β-lactoglobulin is sufficient to form β-lactoglobulin-χ-casein complexes, which result in a deterioration in the suitability of the milk for cheese production. This deterioration is manifested by prolonged coagulation times and reduced firmness of the curd;

- depletion of milk in terms of milk serum proteins or removal of seroproteins is another means of reducing the formation of complexes between β-lactoglobulin and χ-casein.

To the applicant's knowledge, the removal of seroproteins from milk before thermal treatment has been achieved in only one way, namely by exclusion and/or ion exchange chromatography.

Such a process is described in patent FR-A-2 465 422. According to this patent, milk is subjected to a partial or total removal of seroproteins by exclusion and/or ion exchange chromatography before the milk is heated to high temperatures. The industrial application of this process is very difficult because a liquid as clogging as milk must be passed over a chromatography support. This process also encounters ecological limitations linked to the regeneration of the resin columns and, in addition, passing the milk through resins leads to the retention of minerals, which significantly modifies the protein-mineral balances known to play an essential role in the transformation into cheese.

On the other hand, the microfiltration of milk through membranes with pore diameters of 0.2 µ has already been carried out experimentally by J. FAUQUANT, J. L. MAU- BOIS , A. PIERRE (1988), Microfiltration du lait sur membrane minérale. La Technique Laitière, 1028, 21-23.

The authors of this publication simply show that the treatment of skim milk by passing it through a microfiltration membrane to separate it into two liquids a microfiltrate freed from lipids and containing most of the milk serum proteins and a retentate enriched with micellar casein.

Although it is mentioned that the retentate of this microfiltration can constitute a new raw material for cheese production, no information is given about subsequent thermal treatment. This publication actually concerns a preparative milk protein process. It in no way teaches the possibility of thermally treating the retentate of microfiltration, no doubt because a person skilled in the art would assume that such a treatment would have a detrimental effect on the suitability for conversion into cheese. This publication also does not teach the technical possibility of diafiltration of a thermally treated microfiltration retentate with an ultrafiltrate of milk.

Patent FR-A-24 42 592 is based on applying two stages of action of rennet on milk to the ultrafiltration retentates, a well-known phenomenon, where at low temperatures (2ºC - 4ºC) only the enzymatic hydrolysis of the casein takes place; the aggregation of the casein micelles thus hydrolyzed takes place very slowly. Patent FR-A-2 442 592 proposes the addition of warm water to the ultrafiltration retentates in order to raise the temperature of the mixture to the temperatures of coagulum formation (30-40ºC), but it does not teach the liberation of seroproteins or the thermal treatment of the microfiltration retentate.

The article by Bastian et al., Journal of Dairy Science, Volume 74, No. 8, August 1988, describes the distribution of milk components during an ultrafiltration process, which is a technique that is fundamentally different from microfiltration. Microfiltration is a particle-macromolecule separation technique; ultrafiltration separates macromolecules from micromolecular solutes (for example, the separation of proteins and sugars). In addition, the publication by Bastian et al. does not teach in any way how to free milk from seroproteins.

Consequently, the state of the art does not provide a process which involves thermal treatment of milk in a reliable and industrially applicable manner and which allows its suitability for cheese production to be retained.

The applicant has therefore set itself the task of developing a process that makes it possible to obtain milk that not only has good microbiological quality, but also retains its suitability for the production of cheese.

According to the invention, it has surprisingly been found that the removal of seroproteins from milk by microfiltration or that the combination of the steps of removal of seroproteins by microfiltration and concentration by ultrafiltration makes it possible to obtain milk which, after a single thermal treatment, is well suited to the production of cheese.

In the present description, the term suitability for making cheese means the suitability of milk to form curds or coagulates.

The present invention therefore relates to a process for treating milk and other dairy raw materials suitable for being converted into cheese, the process enabling at least their suitability for the production of cheese to be maintained, in particular the coagulation time and the firmness of the coagulates, and is characterized in that the milk is freed of seroproteins by microfiltration and then subjected to thermal treatment.

The process according to the invention may further comprise a step in which the retentates from the microfiltration of milk are treated by ultrafiltration.

In this case, various embodiments of the invention are possible.

According to a first embodiment, ultrafiltration is carried out after the thermal treatment.

According to another embodiment, ultrafiltration is carried out between microfiltration and thermal treatment.

In this description, for the sake of simplicity, the term milk is used to designate the raw material treated. It can therefore be milk or any other dairy raw material capable of being transformed into cheese.

According to the invention, whole or skimmed milk, milk enriched with fat or buttermilk can be treated. The milk can come from all milk-producing female animals: the cow, the goat, the female sheep, the donkey, the buffalo, and the milk from these can be used individually or in a mixture.

Preferably, the milk is microfiltered by diafiltration. Furthermore and preferably, the microfiltration membranes have a pore diameter between about 0.05 µm and 0.50 µm and preferably between about 0.10 µm and 0.20 µm.

The permeation of soluble proteins is facilitated by the practice of diafiltration of milk during microfiltration. The diafiltration technique is well known to those skilled in the art: see, for example, A. R. COOPER, R. G. BOOTH (1980), Demetallation of chelating polymers by diafiltration in the presence of a permeable complexing agent. Ultrafiltration membrane and applications. Edited by A. R. COOPER. Polymer Science and Technology.

The product used for diafiltration can be either, in the case where one wishes to reduce the content of lactose or soluble mineral salts in milk, water or a liquid whose composition corresponds approximately to that of the soluble phase of milk (ultrafiltration permeate).

Depending on the volume of diafiltrate used, the degree of seroprotein liberation obtained for the milk can be up to 100%. It depends on the intensity of the treatment. To illustrate, continuous diafiltration carried out with a volume of diafiltrate equal to 1.2 times the volume of milk used as the starting material leads to a depletion of the content of soluble proteins by 40%, which corresponds to a reduction in the amount of β-lactoglobulin and α-lactalbumin by 60%. Similarly, if the volume of diafiltration is equal to 3 times the volume of milk used as the starting material, the degree of seroprotein liberation achieved is 60%, which corresponds to a reduction in the amount of β-lactoglobulin and α-lactalbumin by 80%.

After partial or complete removal of seroproteins, the milk can be subjected to any thermal treatment that leads to up to 100% denaturation of the soluble proteins.

The thermal treatment is generally carried out for a few fractions of a second to 100 s at a temperature between approximately 90 ºC and 160 ºC, but can also be carried out at lower temperatures if the pressure is lower than atmospheric pressure, as in the case of thermal concentration in an evaporator.

In practical terms, the thermal treatment of milk can be carried out in a heat exchanger, in a thermal evaporator or in a completely different thermal treatment system.

The expert can select the time and temperature conditions characteristic of the thermal treatment through routine tests in order to obtain the desired bacteriological and hygienic quality in accordance with the raw material being treated.

Ultrafiltration is preferably carried out on membranes having a rejection threshold between 10 kD and 30 kD and preferably of about 20 kD.

The suitability of milk for making cheese can be determined by various instruments that measure the formation and development of jellies during coagulation. Among these, one can mention the device commercialized under the name FORMAGRAPH (Foss Electric). Using this device, it is shown that milk depleted of 80% of β-lactoglobulin according to the invention and then heated to 140 ºC for 10 s has a coagulation time of 21 min, while the same milk simply heated to 140 ºC for 10 s does not coagulate after an observation period of 1 h after the addition of rennet.

The study of the parameters of formation and firmness of the curd underlines an improvement in the setting speed and the firmness of the curd obtained by this process, compared to raw milk.

For the expert, these two parameters are representative of the suitability of the milk for making cheese.

The rate of formation of the gel obtained from milk depleted of 40% of its soluble proteins, heated to 140 ºC for 10 s and then concentrated 1.8 times, is increased by 10% compared to that of raw milk. An improvement in the firmness of the curd resulting from this process is also noted. The firmness increases by 20%.

The results obtained by the process according to the invention aim to confirm that the suitability of heated milk for the production of cheese is limited by the content of denatured, soluble proteins and that the removal of seroproteins from raw milk helps to improve its coagulability.

As an example, milk that has not been thermally treated and has undergone a partial removal of 40% of the seroproteins has a better coagulation capacity than the reference milk. The coagulation time is reduced by 5%, the rate of gel formation and the firmness are each increased by 10%.

The method according to the invention therefore enables:

- the production of powders with a high bacteriological quality and a high value for cheese making, obtained by drying microfiltration retentates (concentration factor less than or equal to 3) or by drying microfiltered milk. This use of dried milk for cheese production reveals considerable economic importance, particularly in warm countries where no milk is produced.

- the use of sterile milk for traditional cheese-making technology or for cheese-making technology involving ultrafiltration.

Furthermore, it should be noted that the process described in this invention does not alter the content and distribution of the other constituents of the milk when diafiltration is carried out with the ultrafiltration permeate. It is also possible to alter the mineral salt and lactose content by diafiltering the milk with water.

The products obtained by the process of the invention differ from the conventional products which have not been subjected to microfiltration in that, in the first stage of their transformation into cheese, the initial rate of release of casein macropeptide (CMP) is higher than in the conventional case.

The CMP can be quantitatively determined using the analytical method of J. LEPNIL and D. MOLLE, J. Dairy Res. 58-3, pages 321-328 (1991).

The present invention is illustrated by the following description and the attached drawings in which:

- Figure 1 shows the evolution of the parameters of suitability and coagulation of milk (on the ordinate) as a function of the diafiltrate volume (on the abscissa) according to Example 1.

- Figure 2 is a diagram corresponding to an embodiment of the invention in which the milk (1) is subjected to a microfiltration-diafiltration (2), then to a thermal treatment (3) and finally to an ultrafiltration (4), whereby a product (5) is obtained.

- Figure 3 is a diagram corresponding to an embodiment of the invention in which the milk (1) is subjected to a microfiltration-diafiltration (2), then to an ultrafiltration (4) and finally to a thermal treatment (3) to obtain the product (5).

- Figure 4 is a diagram corresponding to an embodiment of the invention in which the milk (1) is subjected to microfiltration-diafiltration (2) and then to a thermal treatment (3) to obtain the product (5).

EXAMPLE 1: Study of milk coagulation as a function of the content of soluble proteins.

Raw milk was freed from seroproteins by microfiltration according to the invention.

It was measured:

- the clotting time in min (R),

- the time (in minutes) required after the flocculation point to obtain a distance of 20 mm on the previously mentioned "Formagraph" apparatus (K20).

- the distance in mm between the two branches of the rheogram 30 min after addition of the rennet (a 30).

K20 is inversely proportional to the rate of fracture formation, with the value a 30 corresponding to the strength of the resulting coagulum.

Figure 1 shows the evolution of these parameters as a function of the diafiltrate volume.

The larger the diafiltrate volume, i.e. the more significant the liberation of seroproteins, the firmer the resulting coagulum.

EXAMPLE 2: Production of milk.

A skimmed milk is heated to 50 ºC and then continuously diafiltered through a 1.6 m² SFEC S 2*37 module equipped with CARBOSEP-M 14 membranes with a pore diameter of 0.14 µm. The feed rate is 1800 1/h, the milk circulation rate is 7500 l/h, the cleaning rate is 4 m/s. The pressure is approximately 3 bar at the inlet of the module and 0.5 bar at the outlet.

The diafiltrate used is an ultrafiltration permeate of milk at the initial pH obtained through a CARBOSEP M 5 membrane (rejection threshold 10 000 Daltons), their contents not exceeding 0.3 g/l of β-lactoglobulin and 0.1 g/l of α-lactalbumin.

The amount of diafiltrate introduced to eliminate 60% of β-lactoglobulin and α-lactalbumin is 1.2 times the volume of milk used as starting material. To remove 90% of each of these two proteins, it is 3 times the volume of milk used initially.

The milk obtained at the end of diafiltration is sterilized using a Laguilharre UHT apparatus with a steam chamber. Preheating takes place at 80 ºC for 80 s. The sterilization temperature is 140 ºC and is applied for 10 s. From the steam chamber, the milk passes into the relaxation chamber to be cooled directly to 80 ºC, then into the cooling device where the temperature is set at 50 ºC.

The milk is then concentrated twice by ultrafiltration through a 1.6 m² SFEC S 2*37 module equipped with CARBOSEP-M4 membranes with a retention threshold of 20 000 Daltons.

The respective compositions of different products (raw milk, microfiltered-diafiltered milk, microfiltered-diafiltered and sterilized milk, microfiltered-diafiltered, sterilized and concentrated milk) obtained in a test are given in Table I below.

EXAMPLE 3: Production of powder.

The product of Example 2 is evaporated in a Laguilharre experimental evaporator until a dry extract of the product of 30% is obtained. The temperature at the top of the evaporator is less than 70 ºC. The product is then dried in an experimental tower, the inlet temperature being 160 ºC.

EXAMPLE 4: Variant of milk production; extraction of powder.

A skimmed milk is heated to 50 ºC and then continuously diafiltered through a 1.6 m² SFEC module S 2*37 equipped with CARBOSEP-M 14 membranes with a pore diameter of 0.14 µm. The feed rate is 1800 l/h, the milk circulation speed is 7500 l/h, the cleaning speed is 4 m/s. The pressure at the inlet of the module is about 3 bar and 0.5 bar at the outlet.

The diafiltrate used is an ultrafiltration permeate of milk at the initial pH obtained through a CARBOSEP M 5 membrane (rejection threshold 10 000 Daltons), their contents not exceeding 0.3 g/l of β-lactoglobulin and 0.1 g/l of α-lactalbumin.

The amount of diafiltrate introduced to eliminate 60% of β-lactoglobulin and α-lactalbumin is 1.2 times the volume of milk used as starting material. To remove 90% of each of these two proteins, it is 3 times the volume of milk used initially.

The product is then evaporated in a Laguilharre experimental evaporator until a dry extract of the product of 30% is obtained. The temperature at the top of the evaporator is less than 70 ºC. The product is then dried in an experimental tower, the inlet temperature being 160 ºC.

EXAMPLE 5: Reconstitution of milk from the powder obtained according to Example 3 or 4.

The reconstitution of milk from the powder obtained according to Example 3 or 4 is carried out in such a way as to obtain a dry, defatted extract of reconstituted milk of 120 g/kg, which corresponds to a total content of nitrogenous constituents of 45 g/kg.

If part of the phosphate and calcium are rendered insoluble during subsequent thermal treatments it is recommended to add a dose of 0.8 g/kg of calcium hydrogen phosphate to restore mineral balance.

EXAMPLE 6: Production of a Camembert-type cheese.

The milk is prepared as described in Examples 2 or 5. After standardization to 35 g/l fat, this milk, inoculated with 1% mesophilic cultures, is pre-matured for 20 hours at 14 ºC. Penicillium caseicolum is added to the milk.

The next day, the day of production, the milk is heated to 33 ºC and then a variable dose of mesophilic cultures is added depending on the results of the pre-ripening.

The target pH when adding rennet is 6.20. Once this is reached, rennet is added to the milk at a dose of 20 ml per 100 l of milk. The coagulation time is 8 min and the setting time is 45 min. When the curd exudes on the surface, a rough trim is carried out using a cheese cutter.

The curd is then shaped, then turned 7 hours after shaping and on the day following production.

The pH of the cheese is then 4.7 and its total dry matter is 40%. The cheese is then repeatedly smeared and then left to mature. It behaves in the same way as traditional products, and in particular its organoleptic qualities are comparable to those of existing products.

EXAMPLE 7: Production of a Tomme-type cheese.

The milk is prepared as described in Examples 2 or 5.

The milk, whose fat content is standardized to 28 g/l and whose soluble protein content is reduced by half by diafiltration, is sterilized at 117 ºC for 15 s and then concentrated 1.6 times by ultrafiltration.

The milk produced in this way is inoculated with mesophilic homofermentative cultures at a dose of 1% and thermophilic cultures at a dose of 0.5%. Pre-ripening lasts 16 hours at 10 ºC.

The following day, the day of production, the pH of the milk is 6.65. The milk is heated to 33 ºC and is reinoculated with homofermentative lactic acid bacteria at a dose of 1%. After 30 minutes of maturation by heating, the actual pH for the addition of rennet is reached: 6.55. A dose of rennet equivalent to 30 ml/100 l is then added to the milk at 33 ºC. The coagulation time is 25 minutes and the setting time is 12 minutes.

The coagulum is cut using a cutting frame, with the speed of rotation gradually increasing until a grain with an edge length of about 0.7 cm is obtained. The cutting time is 5 minutes. The subsequent stirring is carried out rapidly due to the weak ability of the serum to exude. It takes about 30 minutes.

The blended mixture and the serum are then transferred to a drainage vessel, in which the curd is in a room heated to 25 ºC for 30 minutes at 10 g/cm². The cheese is then shaped and pressed for 4 hours 30 minutes, with an initial pressure of 50 g/cm² for 30 minutes and then 150 g/cm² for 4 hours. The pH of the curd is then 5.20. The cheese is then salted and placed in a salt bath.

The total dry matter content of the cheese is 48%, the total nitrogen content is 24.7% and the pH is 5.10.

One month after production, the cheese shows no organoleptic defects compared to comparable commercial cheese.

EXAMPLE 8: Production of an Emmental-type cheese.

The milk is prepared in the same way as in examples 2 or 5. The milk, adjusted to 28 g/l fat and heated to 33 ºC, is inoculated with 0.5% mesophilic homofermentative cultures, 0.5% thermophilic streptococci and 0.05% thermophilic lactic acid bacteria.

The ripening process takes about 45 minutes and the pH value is then 6.60. The milk is then fermented at a temperature of 33 ºC with a dose of 20 ml rennet per 100 l of milk.

The clotting time is 30 min, the setting time is 6 min.

The blending is done gradually because the curd exudes less serum than in conventional production.

The first stirring of 10 minutes is carried out gently to ensure the integrity of the broken grains. The coagulum is then heated to 54 ºC for 35 minutes and then stirred for 25 minutes. When the When the curd is sufficiently coherent, the serum is drained and the cheese is molded. It is then pressed for 12 hours at 60 g/cm2. The pH of the cheese when removed from the mold is 5.20 and its total dry matter content is 60%. After being placed in a brine bath, the cheese is left to mature under the usual conditions of the technology for producing cheese with pressed cooked dough. The organoleptic qualities of cheese obtained by this process are equivalent to those of cheese obtained in the traditional way.

In the foregoing description, the process of the invention has been illustrated by carrying out microfiltration with diafiltration of the raw material. It is understood, however, that microfiltration can be used without diafiltration. TABLE 1: Composition of products obtained from a milk production experiment.

A: Reference raw milk.

B: Milk depleted of 55% soluble proteins.

C: Milk depleted of 55% soluble proteins and then heated to 140 ºC for 10 min.

D: Milk depleted of 55% soluble proteins, heated to 140 ºC for 10 min and concentrated 1.8-fold by ultrafiltration.

Claims (8)

1. Process for treating milk and other dairy raw materials suitable for being converted into cheese, the process enabling their suitability for cheese production or their coagulability to be maintained or improved and characterized in that the milk is freed from seroproteins by microfiltration and is then subjected to a thermal treatment. 2. Process according to claim 1, characterized in that it further comprises an ultrafiltration step. 3. Process according to claim 2, characterized in that the ultrafiltration is carried out after the thermal treatment. 4. Process according to claim 2, characterized in that the ultrafiltration is carried out between the microfiltration and the thermal treatment. 5. Process according to one of claims 1 to 4, characterized in that the milk is microfiltered by diafiltration. 6. Process according to one of claims 1 to 5, characterized in that the microfiltration is carried out on membranes with a pore diameter between 0.05 µ and 0.50 µ and preferably between 0.10 and 0.20 µ. 7. Process according to one of claims 1 to 6, characterized in that the thermal treatment of the microfiltration retentate is carried out for about a few fractions of a second to 100 s at a temperature between about 90 °C and 160 °C or, if the pressure is lower than atmospheric pressure, at lower temperatures. 8. Process according to one of claims 2 to 7, characterized in that the ultrafiltration is carried out on a membrane with a retention threshold between 10 kD and 30 kD and preferably about 20 kD.